Repatternable nanoimprint lithography stamp

ABSTRACT

A repatternable nanoimprint lithography stamp includes a magnetic substrate and magnetic core nanoparticles. The magnetic substrate includes a magnet and a magnetic mask, and the magnetic core nanoparticles are arranged in a pattern on a surface of the magnetic substrate. The pattern is defined by selective application of a magnetic field to the magnetic substrate using the magnet and the magnetic mask.

BACKGROUND

Nanoimprint stamping is a process that is used to fabricate nano-sizedfeatures and patterns. Generally, nanoimprint stamping creates amechanical deformation in a substrate material that has been heatedabove the glass transition temperature of the substrate material.Nanoimprint stamping is a commonly employed technique for nanoimprintlithography. Typically, stamps are made with a single pattern, requiringmultiple stamps in order to form different architectures across asurface.

SUMMARY

According to an embodiment, a repatternable nanoimprint lithographystamp is disclosed. The repatternable nanoimprint lithography stampincludes a magnetic substrate and magnetic core nanoparticles. Themagnetic substrate includes a magnet and a magnetic mask, and themagnetic core nanoparticles are arranged in a pattern on a surface ofthe magnetic substrate. The pattern is defined by selective applicationof a magnetic field to the magnetic substrate using the magnet and themagnetic mask.

According to another embodiment, a process includes forming a patternedmagnetic substrate that includes magnetic core nanoparticles arranged ina pattern on a surface of a magnetic substrate. The magnetic substrateincludes a magnet and a magnetic mask, and the pattern of the magneticcore nanoparticles is defined by selective application of a magneticfield to the magnetic substrate using the magnet and the magnetic mask.The process also includes utilizing the patterned magnetic substrate asa repatternable nanoimprint lithography stamp.

According to another embodiment, a nanoimprint lithography process isdisclosed. The process includes forming a patterned magnetic substratethat includes magnetic core nanoparticles arranged in a first pattern ona surface of a magnetic substrate. The magnetic substrate includes amagnet and a magnetic mask, and the first pattern of the magnetic corenanoparticles is defined by selective application of a magnetic field tothe magnetic substrate using the magnet and the magnetic mask. Theprocess also includes utilizing the patterned magnetic substrate toperform a first nanoimprint lithography stamping operation. The processfurther includes removing the magnetic core nanoparticles from thesurface of the magnetic substrate by reversing a polarity of themagnetic field. The process also includes forming a second patternedmagnetic substrate that includes magnetic core nanoparticles arranged ina second pattern on the surface of the magnetic substrate. The processfurther includes utilizing the second patterned magnetic substrate toperform a second nanoimprint lithography operation.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the formation of a repatternablenanoimprint lithography stamp, according to one embodiment.

FIG. 2 is a chemical reaction diagram illustrating optional surfacemodification of magnetic core particles of the repatternable nanoimprintlithography stamp in order to generate a lubricious surface on themagnetic core particles, according to one embodiment.

FIG. 3 is a chemical reaction diagram illustrating optional surfacemodification of magnetic core particles of the repatternable nanoimprintlithography stamp in order to generate a lubricious surface on themagnetic core particles, according to one embodiment.

FIG. 4 is a flow diagram showing a particular embodiment of a process offorming a repatternable nanoimprint lithography stamp.

DETAILED DESCRIPTION

The present disclosure describes repatternable nanoimprint lithographystamps and processes of forming repatternable nanoimprint lithographystamps. In the present disclosure, particles containing a magnetic coreare used to pattern a rigid stamp for nanoimprint lithography. Theparticles are easily attracted to a magnetic surface that is used tohold the feature pattern in place. Once that pattern has been placed,the pattern can easily be changed by reversing the polarity of themagnetic surface to liberate particles from that surface. The surfacemay then be re-magnetically charged to promote adhesion of new particlesto the surface in a different pattern or to refresh the original patternwith new particles to promote improved feature definition.

Stamps made from silicon, nickel, soft polymers, polymers, and quartzlack the ability to generate pattern changes as several individualstamps are needed in order to generate different patterns. For example,if a circular pattern is desired, a pattern that is shaped like a circlewould be used. If a square pattern is desired, then a square nanoimprintstamp would be used. By contrast, the present disclosure describesrepatternable nanoimprint stamps that may be generated on an as-neededbasis and that can be refreshed as needed.

In the present disclosure, magnetic core particles (e.g., magneticcore-silica particles) are generated having either a porous ornon-porous surface. Porosity of the surface may allow for high surfacearea features to be generated, as the pores act as a stamping feature aswell. Porous particles can be generated having pore size up to 30 nmusing known techniques such as processes to form mesoporous silicananoparticles (e.g., SBA-15). Magnetic core particles with a silicashell can be generated via a modified Stöber preparation where analkoxysilane, catalyst, and water are used to generate a shell aroundthe magnetic seed particle. Shell thickness can be tailored to improvethe magnetic properties of the particles to ensure that the particleswill magnetically adhere to the magnetic surface. Particle size can betailored by either magnetic seed particle size or by silica shellthickness. Various particle sizes may allow for deeper (largerparticles) or shallower (smaller particles) imprints when used in thestamp application.

In some cases, after particle generation, the particles may be furthersurface modified with a surface lubricating agent in order to generate alubricious surface to prevent the substrate from sticking to thenanoimprint stamp. As an illustrative, non-limiting example,trichloro(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)silanemay be used to post modify the magnetic core particle surface. In othercases, as described further herein, a bridged flourosilane may also beused to prevent sticking of the substrate to the particle surface. Byusing a bridged flourosilane, the kinetics of the reaction drive theflourosilane towards the surface of the particle while the alkoxysilanereacts faster, thus forming the particle shell.

Once the particles have been generated, the particles can be patternedonto a magnetic substrate. The magnetic substrate may allow differentmagnetic patterns to be formed in order to allow the particles to bepatterned. By changing the magnetism on the magnetic substrate, apattern can be formed and changed as desired. As described furtherherein, the repatternable nanoimprint stamps of the present disclosuremay be fabricated using magnetolithography techniques.Magnetolithography is a patterning method based on applying a magneticfield onto a substrate using paramagnetic metal masks. The mask definesthe spatial distribution and shape of the applied magnetic field on thesubstrate. Ferromagnetic nanoparticles are then assembled on thesubstrate according to the field induced by the magnetic mask and beingadsorbed (positive route lithography) or block the surface for furtheradsorption (negative route lithography) at the defined positions.

Referring to FIG. 1, a diagram 100 illustrates an example of a processof forming a repatternable nanoimprint lithography stamp. In FIG. 1, amagnetolithography technique may be used to form a patterned magneticsubstrate (depicted at the top of FIG. 1) that may be utilized as ananoimprint lithography stamp (depicted at the bottom of FIG. 1). Bychanging the magnetism on a magnetic substrate, a pattern can be formed,and metallic core particles may be patterned onto the magneticsubstrate. After reversing the polarity of the magnetic surface toliberate the magnetic core particles, the magnetic surface may bere-magnetically charged to promote adhesion of new particles to thesurface in a different pattern or to refresh the original pattern withnew particles to promote improved feature definition.

The first diagram depicted at the top of FIG. 1 illustrates an exampleof a magnetic substrate 102 that includes a magnet 104, a mask 106, anda substrate 108. The right side of the first diagram illustrates thatmagnetic core nanoparticles 110 (e.g., ferromagnetic silicananoparticles) may be utilized to form a patterned magnetic substrate112 having a pattern of the magnetic core nanoparticles 110 disposed ona surface of the magnetic substrate 102. By selective application of amagnetic field from the magnet 104 via the mask 108, the magnetic corenanoparticles 110 are attracted to the surface of the magnetic substrate102 in order to hold the feature pattern in place.

In a particular embodiment, the magnetic core nanoparticles 110 mayinclude magnetic core-silica particles having either a porous ornon-porous surface. Porosity of the surface may allow for high surfacearea features to be generated, as the pores act as a stamping feature aswell. Porous particles can be generated having pore size up to 30 nmusing known techniques such as processes to form mesoporous silicananoparticles (e.g., SBA-15). Magnetic core particles with a silicashell can be generated via a modified Stöber preparation where analkoxysilane, catalyst, and water are used to generate a shell aroundthe magnetic seed particle. Shell thickness can be tailored to improvethe magnetic properties of the particles to ensure that the particleswill magnetically adhere to the magnetic surface. Particle size can betailored by either magnetic seed particle size or by silica shellthickness. Various particle sizes may allow for deeper (largerparticles) or shallower (smaller particles) imprints when used in thestamp application.

Prophetic Example: Formation of Magnetic Core-Silica Particles viaModified Stöber Process

<Particles are prepared through a modified Stöber synthesis usinganhydrous ethanol (200 proof), ammonia (2M), deionized water, andtetraethoxysilane (TEOS). TEOS is distilled prior to use. Ethanol (5.38mL) and TEOS (0.38 mL) were added to a 20 mL scintillation vial and areshaken to mix. In a separate vial, 2M ammonia (3.75 mL) and deionizedwater (0.49 mL) are added and shaken to mix. To the ammoniacal solution,magnetic nanoparticles (e.g., ferric oxide) (0.114 g) is added. Themagnetic particle/ammoniacal solution is then poured into the monomersolution and shaken for 10 seconds. Vials are then stirred for 24 h.After the reaction period, particles can be centrifuged and rinsed withethanol at least 3 times to remove residual monomer yielding magneticcore-silica nanoparticles>

In some cases, after particle generation, the magnetic corenanoparticles 110 may be further surface modified in order to generate alubricious surface to prevent the substrate 108 from sticking to thenanoimprint stamp. As an illustrative, non-limiting example,trichloro(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)silanemay be used to post modify the magnetic core particle surface. In othercases, as described further herein with respect to FIGS. 2 and 3, abridged flourosilane may also be used to prevent sticking of thesubstrate to the particle surface. By using a bridged flourosilane, thekinetics of the reaction drive the flourosilane towards the surface ofthe particle while the alkoxysilane reacts faster, thus forming theparticle shell.

After particle generation, the magnetic core nanoparticles 110 can bepatterned onto the magnetic substrate 102 to form the patterned magneticsubstrate 112. The magnetic substrate 102 may allow different magneticpatterns to be formed in order to allow the magnetic core nanoparticles110 to be patterned. By changing the magnetism on the magnetic substrate102, a pattern can be formed and changed as desired. Magnetolithographyis a patterning method based on applying a magnetic field onto asubstrate using paramagnetic metal masks. The mask 106 defines thespatial distribution and shape of the applied magnetic field on thesubstrate 108. As shown on the right side of the first diagram depictedat the top of FIG. 1, the magnetic core nanoparticles 110 are thenassembled on the substrate 108 according to the field induced by themagnetic mask 106.

The second diagram depicted at the bottom of FIG. 1 illustrates thepatterned magnetic substrate 112 being utilized as a repatternablenanoimprint lithography stamp 120 to pattern a polymer layer 122disposed on a substrate 124 (e.g., a semiconductor wafer). The patternformed on the polymer layer 122 corresponds to the pattern of themagnetic core nanoparticles 110 adhered to magnetic substrate 112.

While not shown in FIG. 1, after utilizing the repatternable nanoimprintlithography stamp 120 to pattern the polymer layer 122, therepatternable nanoimprint lithography stamp 120 may be removed. Afterremoval, the polarity of the magnet 104 may be reversed to remove themagnetic core nanoparticles 110 from the surface of the magneticsubstrate 102. After reversing the polarity of the magnetic surface toliberate the magnetic core nanoparticles 110, the magnetic surface maybe re-magnetically charged to promote adhesion of new particles to thesurface in a different pattern or to refresh the original pattern withnew particles to promote improved feature definition.

Thus, FIG. 1 illustrates an example of a process of forming arepatternable nanoimprint lithography stamp that includes magnetic corenanoparticles that are arranged in a pattern using a magnetic mask.After utilizing the nanoimprint lithography stamp to form acorresponding pattern in a polymer layer, the polarity of the magneticsurface may be reversed to liberate the magnetic core particles. In somecases, the magnetic surface may be re-magnetically charged in order topromote adhesion of new particles to re-pattern the surface in adifferent pattern. In other cases, the magnetic surface may bere-magnetically charged in order to refresh the original pattern withnew particles to promote improved feature definition.

Referring to FIG. 2, a chemical reaction diagram 200 depicts a firstexample of surface modification of magnetic core particles. Aftergeneration of the magnetic core nanoparticles 110 (as described hereinwith respect to FIG. 1), the magnetic core nanoparticles 110 may befurther surface modified in order to generate a lubricious surface toprevent the substrate 108 from sticking to the nanoimprint stamp.

FIG. 2 depicts an example of the synthesis of a vinyl-bridgedflourosilane using a modified Heck cross-coupling reaction. By using abridged flourosilane, the kinetics of the reaction drive theflourosilane towards the surface of the particle while the alkoxysilanereacts faster, thus forming the particle shell.

Prophetic Example: A Reaction Vessel may be Charged with the Following:

1,4-dibromo-2,3,5,6-tetraflourobenzene (1.0 equiv.);trialkoxy(4-vinylphenyl)silane (>2.0 equiv.); a base, such as calciumcarbonate or potassium carbonate (>2.0 equiv.); a polar aprotic solvent,such as N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF); H₂O, asolution of a palladium catalyst, such as 1-Butanaminium,N,N,N-tributyl-di-μ-bromodibromobis(pent afluorophenyl)dipalladate(2-)(2:1) (CAS #165881-25-4), dihydrogendi-μ-chlorotetrakis(di-tert-butylphosphinito-kP)dipalladate (5 mol %) inthe same solvent as above; a phase transfer agent, such astetrabutylammonium iodide (0.5 equiv.); and an inert atmosphere. Thereaction mixture may be heated to 130° C. and stirred for up to 24hours. The reaction may be monitored by ¹⁹F NMR. Upon completion, themixture may be cooled to room temperature and poured into water. Theaqueous solution may be acidified with 2N HCl and extracted with ether(2X). The extract may be washed with saturated sodium chloride and thendried over anhydrous Na₂SO₄, followed by evaporation of ether, followedby flash chromatography.

Thus, FIG. 2 illustrates an example of a surface modifier for magneticcore particles that can be used to generate a lubricious surface toprevent the magnetic substrate from sticking to the nanoimprintlithography stamp.

Referring to FIG. 3, a chemical reaction diagram 300 depicts alternativeexamples of surface modifiers for magnetic core particles. Aftergeneration of the magnetic core nanoparticles 110 (as described hereinwith respect to FIG. 1), the magnetic core nanoparticles 110 may befurther surface modified in order to generate a lubricious surface toprevent the substrate 108 from sticking to the nanoimprint stamp.

FIG. 3 depicts examples of the synthesis of an ether-bridgedflourosilane. In FIG. 3, the two related ether-bridged flourosilanes areproduced using nucleophilic aromatic substitution of silanefunctionalized phenol on either perflourobiphenyl (depicted in the firstchemical reaction at the top of FIG. 3) or perflourobenzene (depicted inthe second chemical reaction at the bottom of FIG. 3). By using abridged flourosilane, the kinetics of the reaction drive theflourosilane towards the surface of the particle while the alkoxysilanereacts faster, thus forming the particle shell.

Prophetic Example

A reaction vessel may be charged with the following:

hexafluorobenzene or decaflourobiphenyl (1 equiv.); a base, such assodium hydroxide, potassium carbonate, or cesium carbonate (>2.0equiv.); trialkoxy(4-hydroxyphenyl)silane (3.0 eq.); and a polar,high-boiling solvent, such as DMF or DMAc. The reaction mixture may beplaced under an inert atmosphere and heated at 130° C. for 24 hours.Once cooled to room temperature, the mixture may be poured into anexcess of warm (40° C.) water. The resulting solid may be collected byfiltration, and the crude material may be washed with several portionsof warm water (40° C.) and then purified by either recrystallization,sublimation, or column chromatography.

Thus, FIG. 3 illustrates an example of surface modification of magneticcore particles to generate a lubricious surface to prevent the magneticsubstrate from sticking to the nanoimprint lithography stamp.

Referring to FIG. 4, a flow diagram illustrates an exemplary process 400of forming a repatternable nanoimprint lithography stamp, according to aparticular embodiment. In a particular embodiment, the repatternablenanoimprint lithography stamp may correspond to the repatternablenanoimprint lithography stamp 120 illustrated and described furtherherein with respect to FIG. 1.

In the particular embodiment illustrated in FIG. 4, operationsassociated with an example process of forming a patterned magneticsubstrate for use as a nanoimprint lithography stamp are identified asoperations 402-404, while operations associated with the utilization ofthe nanoimprint lithography stamp are identified as operation 406. Itwill be appreciated that the operations shown in FIG. 4 are forillustrative purposes only and that the operations may be performed by asingle entity or by multiple entities. As an example, one entity mayform the magnetic core particles, while another entity may utilize themagnetic core particles to form a patterned magnetic substrate for useas a nanoimprint lithography stamp. Further, while not shown in theexample of FIG. 4, in some cases, the magnetic core nanoparticles may besurface modified in order to generate a lubricious surface to preventthe magnetic substrate from sticking to the stamp (as described furtherherein with respect to FIGS. 2 and 3). In these cases, one entity mayform the magnetic core particles, while the same entity or a differententity may perform operations associated with surface modification ofthe particles.

The process 400 includes forming magnetic core particles, at 402. Forexample, referring to FIG. 1, the magnetic core nanoparticles 110 may beformed via a modified Stöber synthesis procedure, as described furtherherein. In some cases, after particle formation, the magnetic corenanoparticles 110 may be surface modified in order to generate alubricious surface to prevent the magnetic substrate 102 from stickingto the stamp 120 (e.g., as described further herein with respect toFIGS. 2 and 3).

The process 400 includes utilizing magnetolithography to pattern themagnetic core particles onto a magnetic substrate to form a patternedmagnetic substrate, at 404. For example, referring to the diagramillustrated at the top of FIG. 1, the magnetic core nanoparticles 110may be patterned onto the magnetic substrate 102 to form the patternedmagnetic substrate 112.

The process 400 includes utilizing the patterned magnetic substrate as arepatternable nanoimprint lithography stamp, at 406. For example,referring to the diagram illustrated at the bottom of FIG. 1, thepatterned magnetic substrate 112 may be utilized as the repatternablenanoimprint lithography stamp 120 to form a pattern in the polymer layer122.

Thus, FIG. 4 illustrates an example of a process of forming arepatternable nanoimprint lithography stamp. While not shown in theembodiment depicted in FIG. 4, after utilization of the repatternablenanoimprint lithography stamp, the patterned magnetic core particles maybe removed and replaced with other magnetic core particles (in the samepattern or a different pattern).

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A repatternable nanoimprint lithography stampcomprising: a magnetic substrate that includes a magnet and a magneticmask; and magnetic core nanoparticles arranged in a pattern on a surfaceof the magnetic substrate, the pattern defined by selective applicationof a magnetic field to the magnetic substrate using the magnet and themagnetic mask.
 2. The repatternable nanoimprint lithography stamp ofclaim 1, wherein the magnetic core nanoparticles include magneticcore-silica particles.
 3. The repatternable nanoimprint lithographystamp of claim 2, wherein the magnetic core-silica particles are surfacemodified with a surface lubricating agent.
 4. The repatternablenanoimprint lithography stamp of claim 3, wherein the surfacelubricating agent includestrichloro(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)silane.5. The repatternable nanoimprint lithography stamp of claim 3, whereinthe surface lubricating agent includes a bridged flourosilane.
 6. Therepatternable nanoimprint lithography stamp of claim 6, wherein thebridged flourosilane includes a vinyl-bridged flourosilane.
 7. Therepatternable nanoimprint lithography stamp of claim 6, wherein thebridged flourosilane includes an ether-bridged flourosilane.